Non-thermionic glow discharge device having a hollow electrode assembly



MTroS- 3,418,515 ICE HAVING A LY DC 24, 1968 c.. w. A. MASKELL NONTHERMIONIC GLOW DISCHARGE DEV HoLLow FLECTR A MB Filed July 1 6 y 4 f w w 5 1/ J Y Zr? J, 2/ M y 47 ff Nm Nv. .n i x @if/yf m 5 w i W a f/ \f \/f ad 1 lf2 an fa Si? 7 yal. M i( Af/ P f Q x y y f H W. y@ W5 1w @J/ 4 L M\vMmw/////////// 2/ f4 9 my H Z UnitedStates Patent O Claims priority, application Great Britain, July 16, 1965,

30,440/65 12 Claims. (Cl. 313-231) ABSTRACT OF THE DISCLOSURE A non-tbermionic glow discharge device comprising an enclosure, means to maintain the enclosure at a low gas pressure, an anode mounted with at least one suface thereof within the enclosure, and a hollow eletrode assembly, including a cathode and a further electrode are mounted within the enclosure with the ends of the cathode and the further electrode facing each other to define therebetween a generally circular gap. Means -are provided to apply suitable operating potentials to the anode, cathode and further electrode, the arrangement being such that during operation a glow discharge occurs and streams of electrons pass through the gap and converge on the axis of said electrode assembly within a space generally defined by said electrode assembly,

This invention relates to cold cathode, glow discharge devices and more particularly to such devices which form electron sources. v

Such devices can be used, for example, for the heat treatment, welding, drop melting or zone refinement of refractory materials.

According to the present invention, a cold cathode, glow discharge device comprises an enclosure, means to maintain the enclosure at a low gas pressure, an anode mounted within the enclosure or forming part of an interior wall of the enclosure, a hollow electrode assembly mounted within the enclosure, the electrode assembly'including a cathode one end of which is in the shape of a circle, a further electrode mounted within the enclosure one end of the further electrode being in the shape of a circle, said ends of the cathode and the further electrode being adjacent and facing one another so as to define therebetween a generally circular gap, and means to apply suitable operating potentials to the anode, cathode and further electrode, the arrangement being such that during operationg. a glow discharge occurs and streams of electrons pass through the annular gap and converge on the axis of-said electrode assembly within a space generally defined by the said electrode assembly.

The further electrode may be electrically connected to, and form a part of, the cathode, or may be electrically insulated from the cathode and have an operating potential differenttothat of the cathode applied to it. The cathode and the further electrode may both be generally hemispherical or right circular cylindrical. The cathode may include a further outer right circular cylindrical portion formed of wire mesh.

A cold cathode, glow discharge device in accordance with the prese'nt invention will now be described by way of example with reference to the accompanying drawing, in which:

FIGURE 1 shows the device partly schematically and partly in diagrammatic section,

FIGURE 2 shows a modification to the electrode structurc of the device of FIGURE l, and

FIGURE 3 shows a further modification of the electrode structure of thedevice of FIGURE l.

3,418,515 Patented Dec. 24, 1968 Frice Referring now to FIGURE 1 of the drawing, the device comprises an enclosure for-med by a cylindrical tube 1 of heat resisting glass, approximately 23 cm. in diameter and 30 cm. long, closed at the ends by aluminium plates 2 and 3 with O-ring seals (not shown), and supported with its axis vertical. The end plates 2 and 3 are grounded, and in operation of the device form anodes. Within the enclosure is an electrode assembly 4 supported by -an electrically conducting rod 5 which passes up the inside of an electrically conducting tube 6. Outside the anode 2 is an electrically insulating tube 7 which supports a water cooled terminal block 8 to which the rod 5 is connected.

A power supply 9 comprises an auto-transformer which supplies a variable voltage to the primary winding of a high-voltage transformer, the output of which is rectified by a full-wave rectifier. The connection to the block 8 and hence to the electrodeassembly 4 is by way of a resistor 10 which limits the current when the deyice operates in the glow discharge mode. The circuit also includes an ammeter and a voltmeter- (not shown).

Evacuation of the enclosure is by means of an oil diffusion pump backed by a rotary pump, connection to the pumps 11 Ibeing by way-of an outlet pipe 12 passing:

through the anode a. To measure the pressurea Pirani gauge 13 is connected to the outlet pipe 12 immediately outside the enclosure. Helium is supplied from a gas supply cylinder 14 through a two-stage pressure regulator (not shown) and a needle valve 15 to'zan inlet pipe 16 which passes through theY anode 2. The pressure in the enclosure is controlled by adjusting the flow of helium with the pumps 11 .working continuously.

The electrode assembly 4 will now be described in more detail. It comprises two inner hemispherical portions 17 and 18, one forminga part of the cathode and the other forming a part of the further electrode, which are spaced apart and facing j-each other so as to define a generally circular gap 19 between them. Extending from axial apertures inthe portions 17 and 18 are right circular cylindrical portions 20 and 2:1, and secured between the adjacent portions 17 and 20,= `and 18 and 21 are support plates 22 and 23 respectively. Connecting the support plates 22 and 23 are electrically conducting rods 24 which maintain the gap 19. E

The electrode assembly 4. also has an outer right circular cylindrical portion 25 closed by apertured end portions 26 and 27. The support-'plates 22 and 23 are secured to the end plates 2,6 and 27 respectively.

The portions 17, 18, 20, 21and25 to 27 are all formed of stainless steel wire mesh, v'although as an alternative the parts 17 and 18 may beformed of refractory metal plate, for example, tantalumg =plate. The support plates 22 and 23 are formed of refractory metal, for example, tantalum.

The device is operated in the following way. The enclosure is evacuated to a-:pressure of approximately 5.10"3 torr and then filled with lhelium'to a pressure of approximately 5.10-2 torr, this; pressure fbeing maintained by adjusting the valve 15 soi-:that the .gas fiowibalances the capacity of the pumps 11.5 A glow discharge is started `by bringing the electrode assembly 4 to a negative potential of about 2.5 kilovoltsrilnitially, outgassing of the electrode assembly 4 and heating of the gas occurs, but if the pressure is reduced by further restricting-the ow of helium into the enclosure then at a critical pressure of approximately 4.10-2 torr, the glow discharge changes to a hollow cathode discharge accompanied by radial streams of electrons which'passthrough the annular gap 19 and converge on the axis of the electrode assembly 4. The power of the streams of electrons is increased by making the potential of the electrode assembly 4 more negative.

To use the device, the specimen which it is desired to heat is arranged to be mounted within the axially extending aperture in the electrode assembly 4. For example, where a rod of refractory material is to be zone refined, the rod is held in a holder (not shown) which is mounted on a screw thread operable from outside the enclosure, so that the rod can be moved longitudinally through the region of maximum heating on the axis of the gap 19.

The device may of course be used for other purposes, such as heat treatment, welding, drop melting, or zone refining in which heating, particularly the heating of a refractory material, is involved. The device may also be used as a heat source for indirectly heating a further cathode which forms part of an electron beam device for use for example in spot welding.

Various modifications may be made to the device, in particular to the electrode assembly 4, whilst retaining broadly the same operation. Some such modifications will now be briefly described. A

Firstly, although the rods 24 are described as being electrically conductive, thus making the whole of the electrode assembly 4 a cathode, the rods 24 may be made of electrically insulating material, such as alumina, the portion 20 made shorter, the support plates 22 made smaller, and the support plates 22 and the end plates 26 insulated from the cylindrical portion 25 so that portion 17 then becomes a separate, further electrode. A potential dfferent from that applied to the cathode portion 18 may be applied t the portion 17 by way of -a grounded screened connection (not shown). The effect is in the nature of a grid control, in that varying the potential of one portion (further electrode) 17 relative to the cathode portion 18 effects a controlof the discharge and, in particular, causes a defocussing of the stream of electrons passing through the circular gap 19, so resulting in a more diffuse heating effect.

Secondly, and this is shown in FIGURE 2 to which reference is now made, the whole of the outer portions of the electrode assembly 4 can be omitted.

Thirdly, still referring to FIGURE 2, the rods 24 can again be made of electrically insulating material s0 that as Ibefore the portion 17 can be used as a separate, further electrode.

Fourthly, and this is shown in FIGURE 3 to which reference is now made, the cylindrical portions 20 and 21 can be extended to define the gap 19 in place of the hemispherical portions 17 and 18. In this case the support plates 22 and 23 are not required, therods 24 being secured directly to the portions 20 and 21.

Fifthly, still referring to FIGURE 3, the rods 24 can again be made of electrically insulating material so that as before the portion 20 can be used as a separate, further electrode.

Sixthly, still referring ito FIGURE 3, the portion 25 may be provided with an annular gap corresponding in position to the gap 19. In this case the two parts of the portion 25 are secured together by further rods similar to the rods 24.

1. A non-thermionic glow discharge device comprising an enclosure, means to maintain the enclosure at a low gas pressure, an anode mounted with at least one surface thereof within the enclosure, a hollow electrode assembly within the enclosure, the electrode assembly including a cathode, a part of which is in the shape of a segment of a hollow sphere, and a further electrode mounted within the enclosure, a part of which is in the shape of a segment of a hollow sphere, said cathode and said furn ther electrode being arranged so that the concave surfaces of the cathode and the further electrode face eachcathode and further electrode, the' arrangement being such that during operation a glow discharge occurs and streams of electrons pass through the gap and converge on the axis of said electrode assembly within a space generally defined 'by said electrode assembly.

l2. A device in accordance with claim 1 `wherein said electrode assembly includes a further, outer, generally right circular cylindrical portion formed of wire mesh.

3. A device in accordance with claim 1 wherein part of the cathode and the further electrode are both formed of wire mesh. s

4.- A device in accordance with claim 1 wherein pa'rt of the cathode and the further electrode are both formed of refractory metal plate.

5. A device in accordance with claim 1 wherein the further electrode is electrically connected to, and forms a part o'f, the cathode.

6. A device in accordance with claim 1 wherein the further electrode is electrically insulating from said cathode.

-7. A device in accordance with claim 6 wherein a different potential is applied to the further electrode than that applied to the cathode.

8,. A non-thermionic glow discharge device comprising, an enclosure at a low gas pressure, an anode mounted with at least one surface thereof Within kthe enclosure, the electrode including a cathode a part of'which is right circular cylindrical and a further electrode a part of which is right circular cylindrical arranged co-axially with respect to said cathode, said cathode and said further electrode being spaced apart axially to define therebetween a gap, and means to apply suitable operating potentials to the anode, cathode and further electrode, the arrangement being such that during operation a glow discharge occurs and streams of electrons pass through the gap and converge on the axis of said electrode assembly within a space generally defined vby said electrode assembly.

9. A device in accordance with claim 8 wherein saidelectrode assembly includes a further, outer, generally right circular cylindrical portion formed of wire mesh.

10. A device in accordance with claim` 7 wherein the further electrode is electrically connected to, and forms part of, the cathode.

11. A device in accordance with claim 8 wherein the further electrode is electrically insulated from said cathode.

12. A device in accordance with claim 11 wherein a different potential is applied to the further electrode than that applied to the cathode.

J AMES W. LAWRENCE, Primary Examiner.

5/1967 Boring 313-231 X R. L. JUDD, Assistant Examiner.

Us. C1. xa.

7/1966 Allen et al. 313--187' X 

